Method of sterilizing utilizing steam



April 1, 1969 A. LODGE I 3,4363% METHOD OF STERILIZING UTILIZING STEAMFiled Jan. 5. 1965 l2 W STEAM y 33 INVENTOR. 1

A LVI N L0 D G E United States Patent 3,436,170 METHOD OF STERILIZIN GUTILIZING STEAM Alvin Lodge, Erie, Pa., assignor to American SterilizerCompany, Erie, Pa., a corporation of Pennsylvania Filed Jan. 5, 1965,Ser. No. 423,446 Int. Cl. A611 1/00 US. Cl. 21-56 1 Claim ABSTRACT OFTHE DISCLOSURE A process of sterilizing with steam wherein air isremoved from a closed chamber, while simultaneously and intermittentlyintroducing steam to said chamber during said air removal in pulses fora predetermined time, the time between said pulses increasing duringsaid predetermined time, and then introducing steam to said chambercontinuously for sterilization for a time sufficient to effectsterilization of the article.

This invention relates to sterilization and, more particularly, to animproved cycle and apparatus for sterilization of articles.

There have been many methods advocated for promoting rapid steamsterilization of difiicult types of loads. One form of a load which isdifficult to sterilize thoroughly is a surgical pack of cotton fibers,cellulosic material, or the like, which may be wrapped in a form sodense that passage of steam into the pack or air out of the pack ishampered by the fibrous material.

Saturated steam at temperatures above the atmospheric boiling point iswell known as a reliable sterilizing agent. The theory is that theelevated temperature destroys the viability of the bacteria and themoisture introduced by the condensing steam in the process of giving upits latent heat to heat the contaminated material softens or preparesthe bacteria for the kill. To be effective, the steam must reach allparts of the load where sterilizing is required. The presence of air orother non-condensible gas excludes the steam and prevents propersterilization. Air itself is used as a sterilizing medium but it has tobe circulated to all parts of the load by powerful fans and the loadmust be loose and easily penetrated because air has no latent heat togive up at these temperatures and heat is carried by convection only.The absence of moisture makes the bacteria more difficult to kill so airsterilizers use very much higher temperatures.

Excessive temperature and excessive time are both detrimental tocellulosic material. The best sterilizing cycle is the one that subjectsall parts of the load to optimum sterilizing conditions as nearly aspossible at the same instant. This is because, for safetys sake, a delaymust be provided in the control system to equal or exceed any lag thatmay be encountered in the heat-up of the most remote part of the densestpack. Since the more accessible parts will pick up heat rapidly, theseparts will be subjected to high temperatures for a longer time and willbe rapidly damaged.

Common methods for the removal of air and sterilization are the gravitydisplacement, prevacuum, pulsing system, and combinations andmodifications thereof.

The present invention takes advantage of the desirable features ofprevious methods and, in addition, speeds up the process by providing animproved arrangement of piping, valves, and pumps which provide rapidremoval of air from the load.

This sterilizer consists of a pressure chamber with a steam opening nearthe top bafiled to reduce turbulence. A drain opening at the lowestpoint of large dimensions connects with a vacuum source. Means isprovided to intermittently admit steam while the vacuum source isworking.

The vacuum source may consist of a steam ejector connected by largepiping directly to the chamber drain opening and having no valvesbetween the chamber and the ejector. This makes it possible to use asmaller valve. There may be a valve and condenser in the discharge lineof the ejector before discharging into the backup means which may beanother ejector or a vacuum pumping system designed to handle air,water, and water vapor.

The steam line feeding the low pressure ejector may have a drip trap orwater separator at its lowest point to insure dry steam to the ejector.This ejector may be disposed vertically with the steam line and nozzleat the lowest point so that the same drip trap will act as a chamberdrain trap when there is pressure in the chamber and the ejector steamis shut off. The ejector steam valve must be located ahead of the driptrap.

Steam may be intermittently admitted to the chamber by the same steamvalve which is used to admit sterilizing steam. A program of admissionmay be controlled by a cam having grooves representing open positions ofthe valve and lands representing closed positions of the valve. This camcan be revolved at constant speed during the vacuum cycle by a motor andthe spacing of the grooves will determine the frequency of pulses whilethe width of the grooves will determine the duration of each steamadmission.

A cam is shown having six pulses. of equal duration but spaced toprovide large amounts of steam (frequent pulses) early in the cycle andlesser amounts later in the cycle. This intermittent steam pulseprovides a scrubbing action on the load in the sterilizer which helpsremove air from the load while also diluting the air in the chamber.Cams of other land and groove proportions could be provided.

It is, accordingly, an object of the present invention to provide animproved sterilization cycle.

Another object of the invention is to provide a sterilization cyclewhich is simple, efiicient, and effective.

Still another object of the invention is to provide a sterilizingapparatus wherein the use of an improved steam circuit makes it possibleto eliminate certain parts of the apparatus, and, thereby, simplify theapparatus.

A further object of the invention is to provide an improved steamapparatus for sterilization of materials, wherein a notched cam actuatesa mechanism which injects steam in spurts instead of in a steady streamas is frequently done.

Still a further object of the invention is to provide an improvedprogramming apparatus for steam sterilization.

With the above and other objects in view, the invention comprises theprocesses set forth in the specification, drawing, and recited in theappended claim. The invention will be better understood from a referenceto the drawing and detailed specification wherein:

FIG. 1 is a schematic view of a sterilizer having the improved apparatusattached thereto; and

FIG. 2 is an enlarged view of the cam shown in FIG. 1.

Now with more particular reference to the drawing, a sterilizing chamber10 is shown with a steam opening 13 near the top, baffled at 26 toreduce turbulence in the steam entering the chamber. A drain opening 14is provided at the lowest point of the sterilizer. The drain opening isof large dimensions and is connected to a source of vacuum which, in theexample shown, is vacuum pump 19. A means for intermittently admittingsteam while the vacuum pump 19 is operating is shown. This means is madeup of the valve 12, cam 23, and motor M for rotating the cam 23.

The vacuum source may further consist of a steam ejector 15 connected bya large pipe 27 directly to the chamber drain opening 14. It will benoted that no valves or other obstructions are necessary between thechamber and the ejector. This makes it possible to use a smaller valveat 16 in the discharge end of the ejector because here the gas iscompressed and is of smaller volume than in the suction line from thechamber to the ejector where such valves are normally located. Onevariation was made with the vacuum valve situated between the condenserand the pump in order to take advantage of further reduction in volumeof effiuent due to lowered temperature. This was abandoned because offouling of the condenser by sterilizing temperature.

There may be a vacuum valve 18 and a condenser 17 in the discharge line30 from the steam ejector connected in the line before it dischargesinto the backup means which may be either another ejector connected inseries with the ejector shown or the backup means could be vacuum pump19. Pump 19 is designed to handle both air and water or water vapor.

The steam line 31 feeding the low pressure ejector 15 may have a waterseparator 20 and drip trap 21 at its lowest point to insure dry steam tothe ejector 15. This ejector 15 may be disposed vertically in thesuction line with the steam nozzle at the lower end directed upward andconnected with the steam supply through separator 20 which, in turn,drains through trap 21. A check valve 58 should be located in the drainline to prevent return of foreign matter to the chamber when thepressure differential might be reversed. The same drip trap 21 will actas a chamber drain trap when there is pressure in the chamher and theejector steam is shut otf in line 31.

Steam may be intermittently admitted to the chamber through the samesteam valve 12 which is used to admit sterilizing steam. A program ofadmission may be controlled by a cut cam 23 having grooves 24representing open positions of the valve and lands 25 representingclosed positions of the valve. This cam can be revolved at a constantspeed during the vacuum cycle by motor M and the spacing of the grooveswill determine the frequency of pulses while the width of the grooveswill determine the duratio" of each steam admission.

The cam 23 shown has six grooves which are indicated at 24 and each timethe actuating member 33 of the valve 12 drops into one of these grooves24, it turns on the steam in the chamber. This intermittent steam pulseprovides a scrubbing action on the load in the sterilizer which helpsremove air from the load while also diluting the air in the chamber.Thus, by injecting steam in spurts instead of a steady stream, a presetamount of steam is pulsed into the chamber at ditferent intervals,depending on the particular cycle required. After the vacuum cycledescribed above, steam for sterilization may be admitted to the chambercontinuously for a period sufiicient to effect sterilization.

In the illustration shown in FIG. 2, the time between pulses increaseswith rotation of the cam since the grooves are further apart in thedirection of rotation of the cam so that as the steam pressure and thetemperature build up inside the chamber, the time between the pulsesincreases. Thus, the time between pulses can be readily determined by asimple arrangement which is difficult to carry out by other means suchas by means of modulating valves. Also, it is possible to keep thevacuum pump on continuously and no bleed valves are necessary. Also, byuse of the cam, it is not necessary to have additional steam valves forsterilizing steam and the like.

To summarize, the disclosure herein shows an improved cycle forsterilizing and also discloses a simplified piping system thateliminates certain parts that are required in other systems. In additionto the foregoing, no valves are necessary between the chamber and theejector and, by virtue of this, a rapid draw down of the pressurewithout valves is possible. Also, smaller ejector valves are usablewhich is a substantial saving in apparatus cost. Further, the durationof time of the initial part of the cycle is reduced.

The foregoing specification sets forth the invention in its preferredpractical forms but the process disclosed is capable of modificationwithin a range of equivalents without departing from the invention whichis to be understood is broadly novel as is commensurate with theappended claim.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method for sterilizing an article in an enclosed chamber comprisingremoving the air from said chamber at a continuous rate,

simultaneously and intermittently introducing steam to said chamberduring said air removal in pulses for a first predetermined time,

the time between said pulses increasing during said predetermined time,

and introducing steam to said chamber continuously after saidpredetermined time for a period of time sufficient to effectsterilization of said article.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 4/1933 GreatBritain. 10/1953 Great Britain.

MORRIS O. WOLK, Primary Examiner.

BARRY S. RICHMAN, Assistant Examiner.

U.S. Cl. X.R.

